1. Understanding risks to aquatic systems posed by changing drought regimes is particularly important for the conservation of already threatened taxa. However, little is known about how local environmental conditions, especially those in heavily human‐influenced situations, interact with regional shifts such as droughts to alter realised impacts on aquatic communities, including threatened top predators.
2. Here, we investigated the combined effects of stream drying intensity and riparian canopy cover on the trophic interactions of critically endangered kōwaro, or Canterbury mudfish (Neochanna burrowsius) in an agricultural area of New Zealand. Fish populations and their potential prey, both terrestrial and aquatic, as well as environmental variables, including riparian canopy cover and drying measured with stage loggers, were sampled over eight visits to 24 sites spanning orthogonal drying and canopy gradients. Stable isotope ratios, ¹³C/¹²C and ¹⁵N/¹⁴N, were used to investigate trophic links between mudfish and their terrestrial and aquatic prey across these gradients.
3. When non‐native willows (predominantly Salix fragilis) dominated the riparian canopy, increased tree cover led to elevated drying intensity, probably driven by their relatively high water demands compared to other trees. However, in the absence of willows, canopy cover had no effect on drying intensity. Although this was the only direct link between these two environmental factors, they had opposing effects on kōwaro populations, which will be important for management under drought.
4. Increased drying intensity contributed to elevated abundance of microcrustacea and aquatic Diptera larvae, and an increase in the relative abundance of kōwaro juveniles. However, drying‐affected kōwaro populations also had fewer large reproductive adults and elevated δ¹⁵N values, probably driven by physiological limitations and an increase in kōwaro cannibalism, respectively.
5. By comparison, increased canopy cover enhanced input of terrestrial invertebrates, a food resource for larger kōwaro, leading to elevated kōwaro δ¹³C values, no effects on δ¹⁵N values, and higher relative abundance of large kōwaro in shaded streams compared to unshaded streams. Thus, the riparian canopy cover was able to offset some of the effects of drying.
6. Overall, we found no interactions between drying intensity and canopy cover affecting kōwaro. However, their opposing effect highlights the important role local conditions such as riparian canopies play on aquatic communities and their potential role as a restoration tool to mitigate the effects of large‐scale shifts such as drought.

中文翻译：

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弄清溪流干燥和河岸冠层覆盖对高度威胁鱼类的营养生态的多重影响

1. 了解干旱制度的变化对水生系统构成的风险对于保护已经受到威胁的生物分类特别重要。但是，人们对当地的环境条件，特别是那些受人为影响严重的环境条件如何与干旱等区域性变化相互作用，以改变对水生社区（包括受威胁的顶级捕食者）的实际影响的了解甚少。
2. 在这里，我们调查了河流干燥强度和河岸冠层覆盖对新西兰农业区极度濒危的kōwaro或Canterbury泥fish（Neochanna burrowsius）的营养相互作用的综合影响。对鱼的种群及其潜在的猎物，包括陆地和水生鱼类，以及环境变量，包括河岸冠层覆盖度和用阶段记录仪测量的干燥度，进行了八次访问，采样了24个地点，涉及正交干燥和冠层梯度。稳定的同位素比¹³ C / ¹² C和¹⁵ N / ¹⁴ N用于研究在这些梯度下泥fish与其陆生和水生猎物之间的营养联系。
3. 当非本地柳树（主要是脆弱的柳树）在河岸林冠层中占主导地位时，树木覆盖率的提高导致干燥强度的提高，这可能是由于其相对于其他树木的相对较高的需水量所致。然而，在没有柳树的情况下，树冠覆盖对干燥强度没有影响。尽管这是这两个环境因素之间的唯一直接联系，但它们对kōwaro种群产生了相反的影响，这对于干旱条件下的管理非常重要。
4. 干燥强度的增加导致微甲壳纲和水生双翅目幼虫的丰度提高，以及科瓦罗幼鱼的相对丰度提高。然而，干燥-受影响的人群kōwaro也有较少的大生殖成人和升高的δ ^15个N个值，可能是由生理限制驱动并分别增加kōwaro自相残杀。
5. 通过比较，增加了篷盖增强输入陆生无脊椎动物的，食物资源对于较大kōwaro，导致升高的kōwaroδ ^13个C值，对δ无影响^15个N个值，和相对较高的丰度大kōwaro在着色相比无阴影流流。因此，河岸盖可以抵消一些干燥的影响。
6. 总体而言，我们发现干燥强度与冠层覆盖之间没有相互作用影响kōwaro。但是，它们的相反作用凸显了诸如河岸冠层等当地条件对水生社区的重要作用，以及它们作为缓解干旱等大规模变化影响的恢复工具的潜在作用。